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5 - The Chaco Megafans, South America

from Part II - Regional Studies

Published online by Cambridge University Press:  30 April 2023

By
Edgardo M. Latrubesse ,
Edward Park ,
Carlos Ramonell ,
M. Anwar Sounny-Slitine  and
Edgardo Cafaro
Edited by
Justin Wilkinson  and
Yanni Gunnell
Justin Wilkinson
Affiliation:
Texas State University, Jacobs JETS Contract, NASA Johnson Space Center
Yanni Gunnell
Affiliation:
Université Lumière Lyon 2
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Summary

The Chaco plain, covering > 800,000 km2 in Bolivia, Argentina, and Paraguay, comprises six megafans. These are fed mainly from Subandean basins that are among the highest sediment-yielding basins of the Andes: of the total supplied (~ 325 Mt·yr–1) ~ 68 % is trapped on the megafans – because all the rivers except one end on the megafans, reaching at most ~ 50 % of the distance of their late Pleistocene ancestors. As such, the Chaco plain is one of the largest active continental sedimentary sinks of the planet, and includes the longest known megafan. The rivers terminate in the largest area of seasonal wetlands in South America, a product of (i) extremely flat megafan surfaces, (ii) the mosaic of palaeolandforms and present fluvial and lacustrine patterns, and (iii) the hydrogeomorphological dynamics under the current Holocene humid climate. Calculations of specific power appear to explain the effectiveness of these rivers in transporting the current inputs of water and sediment. However, during part of the Late Pleistocene the hydrological and sedimentological regimes allowed the fan-forming rivers to deliver sediment to the regional Paraguay and Paraná trunk rivers and thence to the ocean. New morphometric data describe relationships between feeder-basin area and megafans area, slope and circularity.

Type
Chapter
Information
Fluvial Megafans on Earth and Mars , pp. 78 - 99
Publisher: Cambridge University Press
Print publication year: 2023

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